Tomáš Jarolím

Selected Properties of Cementitous Composites with Portland Cements and Blended Portland Cements in Extreme Conditions

The paper is focused on research of physico-mechanical properties of concretes with Portland-limestone cement, Blastfurnace cement and Portland-composite cement in comparisom with concrete with Portland Cement CEM I. Following physico-mechanical properties of concretes exposed to extreme conditions were tested: compressive strength, flexural strength, tensille splitting strength, velocity of propagation of ultrasonic pulse, dynamic elasticity modulus and density of hardened concrete. Following environments were used in tests: sulphates, magnesic ions, nitrates, gaseous CO2, high temperatures.

Carbon Nanotubes in Cementitious Composites: Dispersion, Implementation, and Influence on Mechanical Characteristics

For effective utilization of nanoparticles in cementitious composite materials, their perfect dispersion is necessary. Appropriate quantity of ultrasonic energy (US energy), as well as usage of proper and compatible surfactant, is a prerequisite for carbon nanotubes’ (CNT) suitable deagglomeration. US energy was supplied by Bandelin Sonopuls HD 3200 ultrasonic homogenizer. Influence of US energy’s amount on CNT’s dispersion in aqueous medium was monitored in two steps: at first roughly by an optical microscope and in the next step precisely by the measurement of absorbance via UV/Vis spectrophotometry. After the appropriate amount of US energy was found, cement mortars with CNT were prepared and tested. Their physical and mechanical properties were examined and compared to the reference specimens.

Study of Effect of Various Types of Cement on Properties of Cement Pastes

This article studies the effect of various types of cement on rheological properties of cement pastes. Rheological properties are significantly related to workability of concrete and to requirements of mixing water amount and thus affect the development of strength, durability of concrete and resistance of concrete to extreme conditions and to high temperature. This article describes the influence of cement type, type and dose of superplasticising admixtures on development of torque in time. Torque was monitored by the rotational viscometer Viskomat NT. Theoretical part of the article briefly describes the phenomenons that can accompany mixing and processing of cement pastes. Experimental part is focused on monitoring the rheological behaviour of cement pastes of different formulas by monitoring the evolution of torque in time.

Influence of CNT Addition to the Frost Resistance of Concrete

Frost resistance of concrete is one of the main durability parameter of Central European climatic conditions. Nanoparticles are the most worldwide examining in materials science. In Brno University of Technology has been interested in nanoparticles for years. First steps were dedicated in identification of nanoparticles (CNT), their dosage and dispersion. After solving before mentioned steps the CNT implementation to concrete could happened. In article was experimentally verify influence of CNT addition to concrete frost resistance after 100 frost cycles. Per results it could be said that addition small dosage of CNT increased frost resistance of concrete.

Nanoadditives - Future of High Performance Concrete

These days it is almost impossible to imagine the technology of high performance concrete without the use of any kind of additive. Whether it is a material capable of achieving high strength, excellent mobility of the fresh mix without losing cohesion or producing high quality architectural concrete surface, microadditives have their certain place for a long time now. Although the research in this field still has something to offer, it does not hurt to try to consider the future and imagine the path that will be taken in the production of high performance concrete of next generation. The article deals with the possibility of using nanoparticles in concrete technology. These materials can actively participate in the creation of very high-quality cement stone. In addition, due to the extreme reactivity of nanoparticles, these reactions can take place almost immediately after the onset of hydration and during its first hours. The experimental part of the paper assesses the impact of nanoparticles on selected properties of fresh cement paste and hardened cement mortar. In all cases, there was a positive effect and it has been demonstrated that nanoparticles may eventually create a new category of high performance concrete additives.